KR102669507B1 - Styrene-based resin compositions, molded products, and light guide plates - Google Patents

Abstract

We provide styrene-based resin compositions with excellent color, transparency, and heat resistance, their molded products, and light guide plates.
A styrene-based resin (A) containing 20 to 80% by mass of styrene-based monomer units and 80 to 20% by mass of (meth)acrylic acid ester-based monomer units, a hindered phenol-based antioxidant (B), and a phosphorus-based antioxidant having a phenolic hydroxyl group. (C1), a styrene-based resin composition containing a phosphorus-based antioxidant (C2) other than C1. When the oxidation induction time measured in an oxygen atmosphere at 200°C is t1, and the oxidation induction time measured in an oxygen atmosphere at 200°C after 500 hours of moist heat treatment in an air atmosphere at 80°C and 90% humidity is t2, t1 is It is preferable that it is 50 minutes or more and that t1-t2 is less than 20 minutes.

Description

Styrene-based resin compositions, molded products, and light guide plates

The present invention relates to a styrene-based resin composition excellent in color, transparency and heat resistance, a molded product thereof, and a light guide plate.

There are two types of backlights for liquid crystal display devices: a direct type in which the light source is placed in front of the display device, and an edge light type in which the light source is placed on the side. Edge light type backlights use a component called a light guide plate that guides light from a light source placed on the side to the front of the display device.

The material for the light guide plate is acrylic resin, such as polymethyl methacrylate (PMMA). However, because PMMA has high water absorption, bending or dimensional changes in the light guide plate may occur due to absorption. In addition, since it is prone to thermal decomposition during molding, there is a problem that appearance defects easily occur in the molded body when molded at high temperatures.

In order to improve this problem, it has been proposed to use styrene-methyl (meth)acrylate copolymer as a material for the light guide plate (for example, see Patent Document 1). In addition, as a technology for improving the color of the styrene-methyl (meth)acrylate copolymer, a technology for mixing blue dye (for example, see Patent Document 2), a technology for limiting the content of the remaining polymerization inhibitor (for example, (see patent document 3) has been proposed.

Japanese Patent Publication No. 2003-075648 Japanese Patent Publication No. 2013-082800 International Publication No. 2016/129675

The object of the present invention is to provide a styrene-based resin composition excellent in color, transparency, and heat resistance, its molded product, and a light guide plate.

That is, the present invention is as follows.

(1) a styrene-based resin (A) having 20 to 80% by mass of styrene-based monomer units and 80 to 20% by mass of (meth)acrylic acid ester-based monomer units, a hindered phenol-based antioxidant (B), and a phenol-based hydroxyl group A styrene-based resin composition containing a phosphorus-based antioxidant (C1) and a phosphorus-based antioxidant (C2) other than C1.

(2) 100 parts by mass of styrene resin (A), 0.001 to 0.3 parts by mass of hindered phenolic antioxidant (B), 0.001 to 0.3 parts by mass of phosphorus antioxidant (C1), and 0.001 part by mass of phosphorus antioxidant (C2) The styrene-based resin composition according to (1) containing ~0.3 parts by mass.

(3) The styrene-based resin composition according to (1) or (2), wherein the content of the phosphorus-based antioxidant (C1) and the phosphorus-based antioxidant (C2) is 3:1 to 1:3 in mass ratio.

(4) The hindered phenolic antioxidant (B) is octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, ethylenebis(oxyethylene)bis[3-( 5-tert-butyl-4-hydroxy-m-tolyl)propionate], pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] The styrene-based resin composition according to any one of (1) to (3), which is at least one selected compound.

(5) Phosphorus-based antioxidant (C1) is 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo The styrene-based resin composition according to any one of (1) to (4), which is [d,f][1,3,2]dioxaphosphepine.

(6) Phosphorus-based antioxidant (C2) is 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus, tris(2,4- The styrene-based resin composition according to any one of (1) to (5), which is at least one compound selected from di-tert-butylphenyl)phosphite.

(7) The YI value at an optical path length of 115 mm is 2.5 or less, and the oxidation induction time measured in an oxygen atmosphere at 200°C is t1, after 500 hours of wet heat treatment in an air atmosphere at 80°C and 90% humidity, The styrene-based resin composition according to any one of (1) to (6), wherein t1 is 50 minutes or more and t1-t2 is less than 20 minutes, assuming that the oxidation induction time measured below is t2.

(8) A molded article using the styrene-based resin composition according to any one of (1) to (7).

(9) A light guide plate using the molded product described in (8).

According to the present invention, a styrene-based resin composition excellent in color, transparency, and heat resistance, a molded product thereof, and a light guide plate can be obtained.

Figure 1 is a conceptual diagram of a method for measuring oxidation induction time by a chemical luminescence method.

In the present specification, the description of “A to B” means more than A and less than or equal to B.

The styrene-based resin composition of the present invention has a styrene-based resin (A), a hindered phenol-based antioxidant (B), a phosphorus-based antioxidant having a phenolic hydroxyl group (C1), and a phosphorus-based antioxidant other than C1 (C2). It is a resin composition.

Styrene-based resin (A) is a copolymer of a styrene-based monomer and a (meth)acrylic acid ester-based monomer.

A styrene-based monomer is an aromatic vinyl-based monomer, and can be used alone or in a mixture of two or more such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, ethylstyrene, and p-tert-butylstyrene. Among these monomers, it is preferable to use styrene from the viewpoint of good color.

(meth)acrylic acid ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, methacrylic acid ester of 2-ethylhexyl (meth)acrylate, methyl acrylate, and ethyl. Acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, and decyl acrylate may be used alone or in a mixture of two or more. From the viewpoint of excellent color and heat resistance, it is preferable to use methyl (meth)acrylate.

The styrene-based resin has a styrene-based monomer unit content of 20 to 80 mass% and a (meth)acrylic acid ester-based monomer unit content of 80 to 20 mass%, preferably a styrene-based monomer unit content of 30 to 60 mass%, The content of (meth)acrylic acid ester monomer units is 70 to 40% by mass. If the content of the styrene-based monomer unit is small, the water absorption rate and strain rate (absorbency) increase, so bending and dimensional deformation may increase due to moisture absorption. If the content of the styrene-based monomer unit is too high, the color may deteriorate or the surface hardness may decrease, making it prone to scratches.

The styrene resin may be copolymerized with monomers other than (meth)acrylic acid ester monomers in an amount of 5% by mass or less. Monomers to be copolymerized include vinyl monomers that can be copolymerized with styrene-based monomers and (meth)acrylic acid ester-based monomers, and include acrylonitrile, methacrylic acid, acrylic acid, and maleic anhydride.

The content of the styrene-based monomer unit and the (meth)acrylic acid ester-based monomer unit of the styrene-based resin can be measured by thermal decomposition gas chromatography under the following conditions.

Pyrolysis furnace: PYR-2A (manufactured by Shimadzu Corporation)

Pyrolysis furnace temperature setting: 525℃

Gas chromatography: GC-14A (manufactured by Shimadzu Corporation)

Column: Glass 3mm diameter × 3m

Filler: FFAP Chromsorb WAW 10%

Column temperature: 120℃

Carrier gas: nitrogen

As a method for producing a styrene-based resin, it can be produced by known bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc. As a method of operating the reaction apparatus, any of continuous, batch (batch), and semi-batch methods can be applied. From the viewpoint of quality such as transparency and productivity, bulk polymerization or solution polymerization is preferable, and continuous polymerization is preferable. Solvents for bulk polymerization or solution polymerization include alkyl benzenes such as benzene, toluene, ethyl benzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane or cyclohexane.

The polymerization method of the styrene resin can be a known method. The radical polymerization method is preferable because it is a simple process and has excellent productivity.

In bulk polymerization or solution polymerization of a styrene resin, a polymerization initiator and a chain transfer agent can be used, and the polymerization temperature is preferably in the range of 110 to 170°C. When performing bulk polymerization or solution polymerization in a continuous manner, from the viewpoint of productivity, it is preferable to carry out the polymerization so that the conversion rate of the styrene-based monomer and (meth)acrylic acid ester-based monomer is 60% or more at the outlet of the polymerization process.

The polymerization initiator is benzoyl peroxide, tert-butylperoxybenzoate, 1,1-di(t-butylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclo. Hexane, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,2-bis(4,4-di-tert-butylperoxy cyclohexyl)propane, tert-butyl Peroxyisopropyl carbonate, dicumyl peroxide, tert-butylcumyl peroxide, tert-butyl peroxyacetate, tert-butylperoxy-2-ethylhexanoate, polyether tetrakis (tert-butylperoxycarbonate), There are organic peroxides such as ethyl-3,3-di(tert-butylperoxy)butyrate and tert-butylperoxyisobutyrate.

The amount of the polymerization initiator added is preferably 0.001 to 0.2% by mass, more preferably 0.001 to 0.05% by mass, based on a total of 100% by mass of monomers. If the amount of polymerization initiator added is too large, the color may deteriorate.

Chain transfer agents include aliphatic mercaptan, aromatic mercaptan, pentaphenylethane, α-methylstyrene dimer, and terpinolene.

The amount of the chain transfer agent added is preferably 0.001 to 0.5 mass%, more preferably 0.005 to 0.2 mass%, based on a total of 100 mass% of monomers. If the added amount of the chain transfer agent is 0.001 to 0.5% by mass, the thermal stability is good.

The devolatilization method for removing volatile components such as unreacted monomers and the solvent used for solution polymerization from the solution after completion of polymerization of the styrene resin can be a known method, for example, a method equipped with a preheater. A vacuum devolatilization bath or a devolatilizing extruder equipped with a vent can be used. The temperature of the styrene resin in the devolatilization process is preferably 200°C to 300°C, and more preferably 220°C to 260°C. If the temperature of the styrene resin in the devolatilization process is too high. The color may deteriorate. The styrene-based resin in a devolatilized molten state is transferred to a granulation process, extruded from a porous die into a strand shape, and can be processed into a pellet shape using a cold cut method, an air hot cut method, or an underwater hot cut method.

It is preferable to recover and purify the unreacted monomers removed in the devolatilization process and the solvent used in solution polymerization to remove impurities such as polymerization inhibitors, and then mix them with fresh raw materials as recovered raw materials. By mixing the recovered raw materials with fresh raw materials that do not contain a polymerization inhibitor, it is possible to reduce the content of the polymerization inhibitor in the raw materials supplied to the polymerization process. The content of the polymerization inhibitor in the raw materials supplied to the polymerization process is preferably less than 12 ppm, more preferably less than 9 ppm, still more preferably less than 6 ppm, and most preferably less than 4 ppm. If the content of the polymerization inhibitor in the raw material supplied to the polymerization process is less than 12 ppm, the transmittance and transparency will be good. Additionally, it is difficult to completely remove the polymerization inhibitor, and it often contains more than 0.01 ppm. Here, fresh raw materials are raw materials newly supplied to the manufacturing process of styrene-(meth)acrylic acid ester-based copolymer, and are referred to as such to distinguish them from recovered raw materials.

Methods for recovering and purifying the unreacted monomers removed in the devolatilization process and the solvent used in solution polymerization can be known methods. For example, the gas of the unreacted monomers and solvents removed in the devolatilization process can be transferred to a condenser. There is a method of condensing, liquefying, and purifying in a flash distillation column to separate and remove the high-boiling point components. In addition, there is a method of first condensing and separating only the high-boiling components from the unreacted monomer and solvent gas removed in the devolatilization process using a condenser or spray tower, and then condensing all of the remaining gas in the condenser. The boiling point of 4-tert-butylcatechol, a polymerization inhibitor, is 285°C, and the boiling point of 6-tert-butyl-2,4-xylenol is 249°C. As a high boiling point component, it can be separated and removed from monomers and solvents ( The boiling point of styrene is 145°C, the boiling point of methyl (meth)acrylate is 101°C, and the boiling point of ethyl benzene is 136°C.

The weight average molecular weight (Mw) of the styrene resin is preferably 50,000 to 450,000, more preferably 70,000 to 300,000, and even more preferably 70,000 to 200,000. If the weight average molecular weight (Mw) is less than 50,000, the strength of the light guide plate may decrease. If the weight average molecular weight (Mw) exceeds 200,000, fluidity may decrease and molding processability may deteriorate. The weight average molecular weight (Mw) can be controlled by the reaction temperature of the polymerization process, residence time, type and amount of polymerization initiator, type and amount of chain transfer agent, type and amount of solvent used during polymerization, etc.

Weight average molecular weight (Mw) can be measured using gel permeation chromatography (GPC) under the following conditions.

GPC model: Shodex GPC-101 manufactured by Showa Denko Co., Ltd.

Column: PLgel 10μm MIXED-B manufactured by Polymer Laboratories.

Mobile phase: tetrahydrofuran

Sample concentration: 0.2 mass%

Temperature: oven 40℃, inlet 35℃, detector 35℃

Detector: Differential refractometer

The molecular weight of the present invention is calculated by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene and calculating the molecular weight in terms of polystyrene.

The total amount of the remaining monomers of the styrene resin and the polymerization solvent is preferably 0.5% by mass or less, and more preferably 0.2% by mass. If the total amount of remaining monomer and polymerization solvent exceeds 0.5% by mass, heat resistance may become insufficient.

The remaining monomer and polymerization solvent are the amount of monomer and polymerization solvent remaining in the styrene resin and include styrene, methyl (meth)acrylate, and ethyl benzene. The amount of remaining monomer and polymerization solvent can be adjusted depending on the configuration of the devolatilization process or the conditions of the devolatilization process.

The amount of remaining monomer and polymerization solvent was determined by precisely weighing 0.2 g of styrene resin, dissolving it in 10 ml of tetrahydrofuran containing p-diethyl benzene as an internal standard, and using capillary gas chromatography. Measured under conditions.

Capillary gas chromatography: GC-4000 (manufactured by GL Sciences Inc.)

Column: GL Sciences Inc. Manufactured by InertCap WAX, inner diameter 0.25 mm, length 30 m, film thickness 50 μm

Injection temperature: 180℃

Column temperature: 60℃ ~ 170℃

Detector temperature: 210℃

Split Ratio: 5/1

It is preferable that the total amount of dimers or trimers (hereinafter referred to as oligomers) of styrene-based monomers and (meth)acrylic acid ester-based monomers of the styrene-based resin is 2% by mass or less. More preferably, it is 1% by mass or less. If the total amount of oligomers exceeds 1% by mass, the heat resistance as a light guide plate may become insufficient.

To measure the oligomer, 200 mg of styrene resin was dissolved in 2 mL of 1,2-dichloromethane, 2 mL of methanol was added, the polymer was precipitated and left to stand, and the supernatant was measured using gas chromatography under the following conditions.

Gas chromatography: HP-5890 (manufactured by Hewlett Packard)

Column: DB-1(ht) 0.25mm×30m, film thickness 0.1μm

Injection temperature: 250℃

Column temperature: 100 ~ 300℃

Detector temperature: 300℃

Split Ratio: 50/1

Internal standard: n-eicosane

Carrier gas: nitrogen

The hindered phenol-based antioxidant (B) contained in the styrene-based resin composition is an antioxidant that has a phenolic hydroxyl group in its basic skeleton. Hindered phenolic antioxidants include octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, ethylenebis(oxyethylene)bis[3-(5-tert-butyl- 4-hydroxy-m-tolyl)propionate], 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1- dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] , 4,6-bis(octylthiomethyl)-o-cresol, 4,6-bis[(dodecylthio)methyl]-o-cresol, 2,4-dimethyl-6-(1-methylpentadecyl)phenol , tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane, 4,4'-thiobis(6-tert-butyl-3-methylphenol) , 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), bis -[3,3-bis-(4'-hydroxy-3'-tert-butylphenyl)-butanoic acid]-glycol ester, 2-tert-butyl-6-(3-tert-butyl-2-hydroxy -5-methylbenzyl)-4-methylphenyl acrylate, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate etc. The hindered phenolic antioxidant may be used alone or in combination of two or more types.

The content of the hindered phenolic antioxidant (B) is preferably 0.001 to 0.3 parts by mass, more preferably 0.03 to 0.15 parts by mass, per 100 parts by mass of the styrene resin (A). By adjusting the content of the hindered phenolic antioxidant (B) to this range, a styrene-based resin composition with excellent color can be obtained.

The phosphorus-based antioxidant (C1) contained in the styrene-based resin composition is a trivalent phosphorus compound having a phenol-based hydroxyl group in the basic skeleton. Phosphorus-based antioxidant (C1) has the characteristic of being easily hydrolyzed compared to other phosphorus-based antioxidants, and has a high color improvement effect of the resulting styrene-based resin composition. Phosphorus-based antioxidant (C1) is 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d, f][1,3,2]dioxaphosphepine, etc.

The content of the phosphorus antioxidant (C1) is preferably 0.001 to 0.3 parts by mass, more preferably 0.03 to 0.15 parts by mass, and still more preferably 0.05 to 0.1 parts by mass, based on 100 parts by mass of the styrene resin (A). . By adjusting the content of the phosphorus-based antioxidant (C1) to this range, a styrene-based resin composition with excellent color can be obtained.

The phosphorus-based antioxidant (C2) contained in the styrene-based resin composition is a trivalent phosphorus compound that does not have a phenol-based hydroxyl group in its basic skeleton. Although the phosphorus-based antioxidant (C2) is less hydrolyzed than the phosphorus-based antioxidant (C1), the color improvement effect of the styrene-based resin composition lasts for a long period of time. Phosphorus-based antioxidant (C2) is 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5 ]undecane, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy) ) Phosphorus, tris (2,4-di-tert-butylphenyl) phosphite, bis [2,4-bis (1,1-dimethylethyl) -6-methylphenyl] ethyl ester phosphorous acid, bis (2,4- di-tert-butylphenyl)pentaerythritol diphosphite, cyclic neopentanetetraylbis(octadecyl phosphite), bis(nonylphenyl)pentaerythritol diphosphite, 4,4'-biphenylenediphosphinic acid tetra Kiss (2,4-di-tert-butylphenyl), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, tetrakis (2,4-di-tert-butyl-5 -methylphenyl)-4,4'-biphenylenediphosphonite, etc., and from the viewpoint of maintaining the color improvement effect, preferably 2,2'-methylenebis(4,6-di-tert-butyl- 1-phenyloxy)(2-ethylhexyloxy)phosphorus or tris(2,4-di-tert-butylphenyl)phosphite can be used. The phosphorus-based antioxidant (C2) may be used alone or in combination of two or more types.

The content of the phosphorus antioxidant (C2) is preferably 0.001 to 0.3 parts by mass, more preferably 0.03 to 0.15 parts by mass, and still more preferably 0.05 to 0.1 parts by mass, based on 100 parts by mass of the styrene resin (A). . By adjusting the content of the phosphorus-based antioxidant (C2) to this range, a styrene-based resin composition with excellent color over a long period of time can be obtained.

The mixing ratio of the phosphorus-based antioxidant (C1) and the phosphorus-based antioxidant (C2) is preferably in the range of 3:1 to 1:3 in mass ratio, more preferably 2:1 to 1:2. By adjusting to this range, the balance between color and durability of the obtained styrene-based resin composition improves.

A known method can be used to produce the styrene-based resin composition. There is a method of adding a hindered phenol-based antioxidant (B), a phosphorus-based antioxidant (C1), and a phosphorus-based antioxidant (C2) in manufacturing processes such as the polymerization process, devolatilization process, and assembly process of styrene resin, and in the devolatilization process, It is preferable to add it after unreacted monomers and solvents have been removed. When using a vacuum deflagellation tank, a molten hindered phenol-based antioxidant (B), a phosphorus-based antioxidant (C1), and a phosphorus-based antioxidant (C2) are added to the styrene-based resin extracted from the deflagellation tank, using a static mixer ( When mixing with a static mixer or using a devolatilizing extruder equipped with a vent, the hindered phenolic antioxidant (B), phosphorus-based antioxidant (C1), and phosphorus-based antioxidant ( C2) can be added and mixed. Using an extruder, a hindered phenol-based antioxidant (B), a phosphorus-based antioxidant (C), and a phosphorus-based antioxidant (C2) may be melt-kneaded with the granulated styrene-based resin (A).

Mineral oil may be added to the styrene-based resin composition as long as transparency is not impaired. In addition, internal lubricants such as stearic acid and ethylenebisstearylamide, and external lubricants such as sulfur-based antioxidants, lactone-based antioxidants, ultraviolet absorbers, hindered amine stabilizers, antistatic agents, and ethylenebisstearylamide may be added. .

Ultraviolet absorbers have the function of suppressing deterioration and coloring caused by ultraviolet rays, and include benzophenone-based, benzotriazole-based, triazine-based, benzoate-based, salicylate-based, cyanoacrylate-based, malonic acid ester-based, and formosa. Ultraviolet absorbers such as amidine series can be mentioned. These can be used individually or in combination of two or more types, and light stabilizers such as hindered amines may be used together.

The Vicat softening point of the styrene resin is preferably 95°C or higher, and more preferably 98°C or higher. If the Vicat softening point is less than 95°C, heat resistance is insufficient, and the molded product may be deformed depending on the usage environment. (The Vicat softening temperature was tested in accordance with JIS K 7206 at a temperature increase rate of 50°C/hr and a test load of 50N.)

For the styrene-based resin composition, the oxidation induction time measured in an oxygen atmosphere at 200°C is t1, and the oxidation induction time measured in an oxygen atmosphere at 200°C after moist heat treatment for 500 hours in an air atmosphere at 80°C and 90% humidity is t2. In one case, it is preferable that t1 is 50 minutes or more and that t1-t2 is less than 20 minutes. t1 is preferably 70 minutes or more, and more preferably 90 minutes or more. Additionally, t1-t2 is preferably less than 10 minutes. If t1 is less than 50 minutes, the color and transmittance of the long optical path may deteriorate due to yellowing in a high temperature environment. If t1-t2 is 20 minutes or more, if the styrene-based resin composition is stored in a high-temperature, high-humidity environment, the color and transmittance of the long optical path after molding may deteriorate. The oxidation induction time of the styrene-based resin composition can be lengthened by increasing the amount of hindered phenol-based antioxidant and phosphorus-based antioxidant. However, if these antioxidants are excessively increased, the color of the styrene-based resin composition may deteriorate.

The oxidation induction time is a value measured by the chemical luminescence method. The change over time in the light emission amount of the styrene resin composition was measured under the following conditions, and from the relationship between the obtained measurement time and the light emission amount, as shown in Figure 1, the time of the intersection of the straight line before the light emission amount changed and the straight line after the light emission amount increased was calculated. When a styrene-based resin composition is heated in the presence of oxygen, it is gradually oxidized. When antioxidants are present in the sample, the antioxidants are gradually consumed by oxidation, but a constant amount of light is emitted as long as the antioxidants are present. When the antioxidant disappears, the resin itself is oxidized and an increase in luminescence is immediately seen. In other words, the oxidation induction time represents the time during which the antioxidant is consumed and oxidation of the resin composition progresses rapidly.

Chemical luminescence meter: CLA-FS4 (manufactured by Tohoku Tenjisangyo)

Measurement temperature: 200℃

Oxygen flow rate: 100mL/min

The styrene-based resin composition can be used by producing a plate-shaped molded article by known methods such as extrusion molding, injection molding, compression molding, and blow molding, and processing it into a light guide plate, etc.

Since the styrene-based resin composition of the present invention has excellent thermal stability, it recovers and pulverizes parts that cannot be commercialized, such as sheet end materials during extrusion molding or spools and runners during injection molding, and converts them into virgin raw materials. Can be used by mixing.

The light guide plate is a member that has the function of guiding light incident from the end face of the plate-shaped molded product to the surface side of the plate-shaped molded product and emitting light through a reflection pattern formed on one side of the plate-shaped molded product. Reflective patterns can be formed by methods such as screen printing, laser processing, or inkjet. Additionally, a prism pattern, etc. can be formed on the surface opposite to the surface on which the reflection pattern is formed (light-emitting surface). The reflection pattern or prism pattern of the plate-shaped molded product can be formed during molding of the plate-shaped molded product, and can be formed by mold shape in injection molding or roll transfer in extrusion molding.

The YI value of the styrene-based resin composition measured at an optical path length of 115 mm is 2.5 or less, and is preferably 2.0 or less. The measurement measures the spectral transmittance at a wavelength of 350 nm to 800 nm at an optical path length of 115 mm, and the YI value at a 2° field of view for a C light source is a value calculated based on JIS K7105. If the YI value measured at an optical path length of 115 mm is higher than 2.5, the color changes with the optical path length, so when used as a backlight, color unevenness may occur on the surface of the liquid crystal display device. In addition, the average value of the spectral transmittance for a wavelength of 350 nm to 800 nm measured at an optical path length of 115 mm is preferably 87% or more, more preferably 88% or more, and even more preferably 89% or more.

Example

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

<Manufacture example of styrene-based resin A-1>

Styrene-based resin was manufactured by radical polymerization and continuous solution polymerization. A polymerization process was constructed by using a completely mixing tank-type agitated tank as the first reactor and a plug flow-type reactor equipped with a static mixer as the second reactor and connecting them in series. The capacity of the first reactor was 30 L, and the capacity of the second reactor was 12 L. As a result of preparing styrene (hereinafter referred to as fresh Sty), which is industrially used as a styrene-based monomer, the concentration of 4-tert-butylcatechol (hereinafter referred to as TBC) was 10.2 ppm. As a result of preparing methyl (meth)acrylate (hereinafter referred to as fresh MMA), which is used industrially as a (meth)acrylic acid ester monomer, 6-tert-butyl-2,4-xylenol (hereinafter referred to as TBX) ) concentration was 4.9ppm. Ethyl benzene (hereinafter referred to as fresh EB), which is used industrially, was prepared as a polymerization solvent. In addition, gases such as monomers and polymerization solvent separated in a vacuum devaporizer described later were condensed in a condenser and purified in a fresh distillation column and used as recovered raw materials. The concentrations of TBX and TBC in the recovered raw materials were below the detection limit. Using fresh Sty, fresh MMA, and recovered raw materials, a raw material solution was prepared with a composition of Sty: 49% by mass, MMA: 41% by mass, and EB: 10% by mass, and the polymerization process was continuously carried out at a flow rate of 8.0kg/hr. supplied. The percentage of recovered raw materials used in the raw material solution was 33% by mass. In addition, t-butylperoxy isopropyl monocarbonate as a polymerization initiator was continuously added to the supply line of the raw material solution at a concentration of 150 ppm, and n-dodecyl mercaptan as a chain transfer agent was added to a concentration of 500 ppm. The temperature of the first reactor was adjusted to 135°C, and in the second reactor, a temperature gradient was provided along the direction of flow, so that the temperature was 130°C in the middle and 145°C in the outlet. The polymer concentration at the outlet of the polymerization process was 65%, and the conversion rate of styrene and methyl (meth)acrylate was 72%. The polymer solution continuously withdrawn from the reactor was supplied to a vacuum devolatilizer equipped with a preheater, and unreacted styrene, methyl (meth)acrylate, ethyl benzene, etc. were separated. The temperature of the preheater was adjusted so that the polymer temperature in the devolatilization tank was 240°C, and the pressure in the devolatilization tank was 1 kPa. The polymer was extracted from the vacuum devolatilizer using a gear pump, extruded into a strand shape, cooled with cooling water, and cut to obtain pellet-shaped styrene-based resin A-1. The composition of A-1 was Sty: 50% by mass, MMA: 50% by mass. In addition, the weight average molecular weight of A-1 was 145,000, the total amount of remaining monomers and polymerization solvent was 0.07% by mass, and the total amount of remaining oligomers was 0.35% by mass.

<Manufacture example of styrene-based resin A-2>

The raw material composition was changed to Sty: 77 mass%, MMA: 13 mass%, and EB: 10 mass%, the addition of n-dodecyl mercaptan was stopped, the temperature of the first reactor was set to 140 ° C., and the middle of the second reactor The same procedure as A-1 was carried out except that the temperature of the part was set to 140°C and the temperature of the outlet part was set to 160°C. The percentage of recovered raw materials used in the raw material solution was 33% by mass. The composition of A-2 was Sty: 82% by mass, MMA: 18% by mass. Additionally, the weight average molecular weight of A-2 was 240,000, the total amount of remaining monomer and polymerization solvent was 0.06 mass%, and the total amount of remaining oligomer was 0.33 mass%.

<Manufacture example of styrene-based resin A-3>

The raw material composition was changed to Sty: 8 mass%, MMA: 79 mass%, EB: 13 mass%, the feed flow rate was 5.7 kg/hr, and the concentration of tert-butylperoxy isopropyl monocarbonate was 100 ppm and n-dodecyl. The same procedure as A-1 was carried out except that the mercaptan concentration was set to 3000ppm, the temperature of the first reactor was set to 122°C, the temperature of the middle part of the second reactor was set to 140°C, and the temperature of the outlet part was set to 150°C. did. The percentage of recovered raw materials used in the raw material solution was 34% by mass. The composition of A-3 was Sty: 10% by mass, MMA: 90% by mass. Additionally, the weight average molecular weight of A-3 was 80,000, the total amount of remaining monomer and polymerization solvent was 0.06 mass%, and the total amount of remaining oligomer was 0.34 mass%.

<Examples 1 to 5 Comparative Examples 1 to 8>

To the styrene-based resins A-1 to A-3 obtained in the production example, the following hindered phenolic antioxidant (B), phosphorus-based antioxidant (C1), and phosphorus-based antioxidant (C2-1), (C2-2) were added. was mixed at the content shown in Table 1 or Table 2, and a sheet molded product of 450 mm x 500 mm x 2 mm was obtained while melting and kneading the antioxidant using a sheet extruder manufactured by LEADER. The sheet extruder was composed of a 50 mm ϕ single-screw extruder, a T die, and three mirror rolls, and sheet extrusion was performed at a cylinder temperature of 225°C and a screw rotation speed of 120 rpm of the single-screw extruder. The width of the T die was 450 mm and the opening was 3 mm.

(B) Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (manufactured by BASF JAPAN Co., Ltd., Irganox 1076)

(C1) 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d,f][1 ,3,2]dioxaphosphepine (Sumitomo Chemical Co., Ltd., Sumilizer GP)

(C2-1) 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus (manufactured by ADEKA Co., Ltd., ADK STAB HP-10)

(C2-2) Tris(2,4-di-tert-butylphenyl)phosphite (manufactured by BASF JAPAN Co., Ltd., Irgafos 168)

(Oxidation induction time)

A test piece of 30 mm From the relationship between measurement time and light emission amount, the oxidation induction time was determined by the method shown in FIG. 1. The measurement results of the oxidation induction time (t1) of the sheet molded product immediately after extrusion and the oxidation induction time (t2) of the sheet molded product subjected to wet heat treatment for 500 hours in an air atmosphere of 80°C and 90% humidity are shown in Table 1 or Table 2. In addition, in Comparative Examples 1 and 5, the amount of light emission increased immediately after the start of measurement, and the oxidation induction time could not be measured.

(Optical characteristics at an optical path length of 115 mm)

A test piece with a thickness of 115 mm x 85 mm x 2 mm was cut from the obtained sheet molded article, and the cross section was polished to create a plate-shaped molded article having a mirror surface on the cross section. For the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by Nippon Bunko Co., Ltd., for incident light with a size of 20 The transmittance was measured, and the YI value at a 2° field of view of the C light source was calculated based on JIS K7105. The transmittance shown in Table 1 and Table 2 represents the average transmittance for a wavelength of 380 nm to 780 nm. Table 1 or Table 2 shows the measurement results for the sheet molded product immediately after extrusion (initial), the sheet molded product subjected to wet heat treatment for 500 hours in an air atmosphere of 80°C and 90% humidity, and the sheet molded product stored for 1000 hours in an environment of 80°C. It appears in

(absorbent)

The obtained sheet molded product was cut to obtain a molded product with a size of 200 mm x 300 mm. This molded product was stored for 500 hours at a temperature of 60°C and humidity of 90%, the change in mass and long side dimension before and after storage was measured, and the water absorption rate and strain rate were calculated using the following formula as an index of water absorption.

(Absorption rate) = ((mass after storage) - (mass before storage)) ÷ (mass before storage) × 100 (%)

(Strain rate) = ((long side length after storage) - (long side length before storage)) ÷ (long side length before storage) × 100 (%)

The evaluation results are shown in Table 1 or Table 2. Cases where the water absorption rate was 1.0 or less were judged to be good, and cases where the strain rate was 0.30 or less were judged to be good.

As shown in Tables 1 and 2, in the Examples in which a hindered phenol-based antioxidant (B), a phosphorus-based antioxidant having a phenolic hydroxyl group (C1), and a phosphorus-based antioxidant other than C1 (C2) were added, the comparative examples Compared to this, it has excellent color and transparency right after molding, and also has little color change and excellent heat resistance under high temperature and high humidity.

Industrial applicability

The styrene-based resin composition of the present invention and its molded product have low water absorption, excellent transparency and color over a long optical path, and are also excellent in durability, so they can be used in TVs, desktop personal computers, laptop-type personal computers, mobile phones, car navigation, It can be suitably used for light guide purposes such as indoor lighting.

Claims (9)

A styrene-based resin (A) containing 20 to 80% by mass of styrene-based monomer units and 80 to 20% by mass of (meth)acrylic acid ester-based monomer units, a hindered phenol-based antioxidant (B), and a phosphorus-based resin having a phenol-based hydroxyl group. A styrene-based resin composition containing an antioxidant (C1) and a phosphorus-based antioxidant (C2) other than the C1. According to paragraph 1,
100 parts by mass of the styrene-based resin (A), 0.001 to 0.3 parts by mass of the hindered phenol-based antioxidant (B), 0.001 to 0.3 parts by mass of the phosphorus-based antioxidant (C1), and the phosphorus-based antioxidant (C2) Contains 0.001 to 0.3 parts by mass,
The content of the phosphorus-based antioxidant (C1) and the phosphorus-based antioxidant (C2) is 3:1 to 1:3 in mass ratio,
The hindered phenolic antioxidant (B) is octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, ethylenebis(oxyethylene)bis[3-(5- tert-butyl-4-hydroxy-m-tolyl) propionate], pentaerythritol tetrakis [3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate]. At least one compound,
The phosphorus-based antioxidant (C1) is 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d ,f][1,3,2]dioxaphosphepine,
The phosphorus-based antioxidant (C2) is 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus, tris(2,4-di- A styrene-based resin composition comprising at least one compound selected from tert-butylphenyl)phosphite. According to paragraph 1,
The YI value at an optical path length of 115 mm is 2.5 or less,
When the oxidation induction time measured in an oxygen atmosphere at 200°C is t1, and the oxidation induction time measured in an oxygen atmosphere at 200°C after moist heat treatment for 500 hours in an air atmosphere at 80°C and 90% humidity is t2, the t1 A styrene-based resin composition in which t1-t2 is 50 minutes or more and t1-t2 is less than 20 minutes. A molded article using the styrene-based resin composition according to claim 1 or 2. A light guide plate using the molded product described in paragraph 4. delete delete delete delete